Epoxy resin compositions having a long shelf life

ABSTRACT

A composition comprising 
     (a) an epoxy resin having, on average, more than one 1,2-epoxy group per molecule, 
     (b) a polyol as epoxy resin curing agent and 
     (c) a solid microgel-amine adduct as accelerator has high latency, good storage stability and a wide processing window.

The present invention relates to compositions comprising an epoxy resinand, as curing agent for the epoxy resin, a polyol and, as accelerator,a microgel-amine salt or microgel-imidazole salt, and also tocrosslinked products obtainable by curing such compositions.

Nitrogen-containing bases are well known to the person skilled in theart as curing agents or curing accelerators for epoxy resins. Suchsystems have, however, only limited storage stability because thosebases react with epoxides even at relatively low temperature, in somecases even at room temperature, which is manifested in an increase inthe viscosity of the epoxy resin formulation and, on prolonged storage,results in gelation of the mixture. The greater the reactivity of thenitrogen-containing base, the lower the storage stability of the epoxyresin mixture and the shorter the pot life. For that reason, suchsystems are formulated as two-component systems, that is to say theepoxy resin and the nitrogen-containing base are stored separately andmixed only shortly before processing.

There has been no shortage of attempts at improving the storagestability of such systems by developing appropriate curing systems. Theproblem posed is the more complex because, at the same time as therequirement for a high storage stability and a long pot life, thereshould not be any deterioration either in the reactivity at the desiredcuring temperature or in the properties of the fully cured materials.

EP-A-304 503 describes masterbatches of encapsulated materials andepoxides as latent curing agents for epoxy resins, wherein the corematerial is a tertiary amine in powder form, which is surrounded by ashell of the reaction product of the same amine with an epoxy resin.

A similar curing system, but with a core material of an amine and ananhydride, is disclosed in JP-A-Hei 02-191624.

Although such latent curing agents and accelerators based onencapsulated particles are suitable for producing storage-stableone-component systems, they have the disadvantage of inadequatestability with respect to mechanical influences, such as shear forcesand compressive loads.

BCl₃ complexes also have good latency, but fumes are formed attemperatures above 160° C., prohibiting their use in epoxy-resin-basedcasting resins because the mould temperatures are at or above thattemperature.

EP-A 0 816 393 describes latent epoxide curing systems (based onanhydride curing agents in combination with salts ofCOOH-group-containing microgels and nitrogen bases) having an improvedpot life, which have high stability with respect to mechanical stress inthe form of shear forces and, in addition, result in cured mouldingsthat have a high glass transition temperature and a high thermalstability. The latency of those systems is, however, capable of furtherimprovement, especially at elevated temperatures.

EP-A 0 633 286 describes curable epoxide curing systems for theproduction of moulded articles having high-gloss surfaces, comprising anepoxy resin, a curing agent and, as fillers, wollastonite and aquartz/kaolinite mixture. The latency of such systems is, however,like-wise capable of further improvement.

The aim of the present invention was to make available epoxide curingsystems having good storage stability, good reactivity under curingconditions, good and at the same time highly varied processingpossibilities, even at elevated temperatures, and, finally, goodproperties of the fully cured materials.

It has now been found that compositions comprising an epoxy resin and,as curing agent for the epoxy resin, a polyol and, as accelerator, asolid microgel-amine salt or a solid microgel-imidazole salt have thedesired property profile.

The present invention accordingly relates to a composition comprising

(a) an epoxy resin having, on average, more than one 1,2-epoxy group permolecule,

(b) a polyol as epoxy resin curing agent and

(c) a solid reaction product of a carboxylic-acid-group-containingmicrogel and a nitrogen-containing base (microgel-amine adduct) asaccelerator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagrammatic view of a compression tool.

FIG. 2 shows a longitudinal section through the coil former used in theExamples, and its dimensions.

FIG. 3 shows a metal core of a coil encapsulated with the moldingcompound so that the outer contour forms a coil former for the innerwinding of a rod-like ignition coil. The black area corresponds to themolding composition

FIG. 4 shows an outer contour of the molding forming a coil former for asecond, complementary winding. The black area corresponds to the moldingcomposition.

FIG. 5 depicts an outer winding that has been impregnated andencapsulated, and in which the outer shape is identical to the outercontour of the rod-like ignition coil. The molding compositioncorresponds to the hatched area.

For the preparation of the compositions according to the invention,epoxy resins suitable as component (a) are those customary in epoxyresin technology. Examples of epoxy resins are:

I) Polyglycidyl and poly(β-methylglycidyl) esters, obtainable byreaction of a compound having at least two carboxyl groups in themolecule with epichlorohydrin and β-methylepichlorohydrin, respectively.The reaction is advantageously performed in the presence of bases.

Aliphatic polycarboxylic acids may be used as the compound having atleast two carboxyl groups in the molecule. Examples of suchpolycarboxylic acids are oxalic acid, succinic acid, glutaric acid,adipic acid, pimelic acid, suberic acid, azelaic acid or dimerised ortrimerised linoleic acid.

It is also possible, however, to use cycloaliphatic polycarboxylicacids, for example tetrahydrophthalic acid, 4-methyltetrahydrophthalicacid, hexahydrophthalic acid or 4-methylhexahydrophthalic acid.

Aromatic polycarboxylic acids, for example phthalic acid, isophthalicacid or terephthalic acid, may also be used.

II) Polyglycidyl or poly(β-methylglycidyl) ethers, obtainable byreaction of a compound having at least two free alcoholic hydroxy groupsand/or phenolic hydroxy groups with epichlorohydrin orβ-methylepichlorohydrin under alkaline conditions or in the presence ofan acid catalyst with subsequent alkali treatment.

The glycidyl ethers of this kind are derived, for example, from acyclicalcohols, e.g. from ethylene glycol, diethylene glycol or higherpoly(oxyethylene) glycols, propane-1,2-diol or poly(oxypropylene)glycols, propane-1,3-diol, butane-1,4-diol, poly(oxytetramethylene)glycols, pentane-1,5-diol, hexane-1,6-diol, hexane-2,4,6-triol,glycerol, 1,1,1-trimethylol-propane, pentaerythritol, sorbitol, and alsofrom polyepichlorohydrins.

Further glycidyl ethers of this kind are derived from cycloaliphaticalcohols, such as 1,4-cyclohexanedimethanol,bis(4-hydroxycyclohexyl)methane or 2,2-bis(4-hydroxycyclohexyl)-propane,or from alcohols that contain aromatic groups and/or further functionalgroups, such as N,N-bis(2-hydroxyethyl)aniline orp,p′-bis(2-hydroxyethylamino)diphenylmethane. The glycidyl ethers canalso be based on mononuclear phenols, for example resorcinol orhydroquinone, or on polynuclear phenols, for examplebis(4-hydroxyphenyl)methane, 4,4′-dihydroxybiphenyl,bis(4-hydroxyphenyl)sulfone, 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane,2,2-bis(4-hydroxyphenyl)propane or2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane.

Further hydroxy compounds that are suitable for the preparation ofglycidyl ethers are novolaks, obtainable by condensation of aldehydes,such as formaldehyde, acetaldehyde, chloral or furfuraldehyde, withphenols or bisphenols that are unsubstituted or substituted by chlorineatoms or by C₁-C₉alkyl groups, e.g. phenol, 4-chlorophenol,2-methylphenol or 4-tert-butylphenol.

III) Poly(N-glycidyl) compounds, obtainable by dehydrochlorination ofthe reaction products of epichlorohydrin with amines containing at leasttwo amine hydrogen atoms. Such amines are, for example, aniline,n-butylamine, bis(4-aminophenyl)methane, m-xylylenediamine orbis(4-methylaminophenyl)methane.

The poly(N-glycidyl) compounds also include, however, triglycidylisocyanurate, N,N′-diglycidyl derivatives of cycloalkyleneureas, such asethyleneurea or 1,3-propyleneurea, and diglycidyl derivatives ofhydantoins, such as of 5,5-dimethylhydantoin.

IV) Poly(S-glycidyl) compounds, for example di-S-glycidyl derivatives,derived from dithiols, e.g. ethane-1,2-dithiol orbis(4-mercaptomethylphenyl) ether.

V) Cycloaliphatic epoxy resins, e.g. bis(2,3-epoxycyclopentyl) ether,2,3-epoxycyclopentyl-glycidyl ether,1,2-bis(2,3-epoxycyclopentyloxy)ethane or 3,4-epoxycyclohexylmethyl3′,4′-epoxycyclohexanecarboxylate.

It is also possible, however, to use epoxy resins wherein the 1,2-epoxygroups are bonded to different hetero atoms or functional groups; suchcompounds include, for example, the N,N,O-triglycidyl derivative of4-aminophenol, the glycidyl ether glycidyl ester of salicylic acid,N-glycidyl-N′-(2-glycidyloxypropyl)-5,5-dimethylhydantoin and2-glycidyloxy-1,3-bis(5,5-dimethyl-1-glycidylhydantoin-3-yl)propane.

In addition to liquid polyglycidyl ether and ester compounds there alsocome into consideration solid polyglycidyl ether and ester compoundshaving melting points above room temperature up to about 250° C. Themelting points of the solid compounds are preferably in the range from50 to 150° C. Such solid compounds are known and, in some cases,commercially available. It is also possible to use as solid polyglycidylethers and esters the advancement products obtained by pre-lengtheningliquid polyglycidyl ethers and esters.

For the preparation of the epoxy resin compositions according to theinvention it is preferred to use an aromatic epoxy resin, that is to sayan epoxy compound having one or more aromatic rings in the molecule.

For the preparation of the epoxy resin compositions according to theinvention, there is especially used a bisphenol diglycidyl ether,optionally pre-lengthened, or an epoxy novolak resin, more especially anepoxy phenol- or epoxy cresol-novolak resin. It is also possible to usemixtures of epoxy resins.

As epoxy resin curing agent (b) for the epoxy resin compositionsaccording to the invention, aliphatic or aromatic polyols are used.

Suitable aliphatic polyols are, for example, ethylene glycol, diethyleneglycol and higher poly(oxyethylene) glycols, propane-1,2-diol orpoly(oxypropylene) glycols, propane-1,3-diol, butane-1,4-diol,poly(oxytetramethylene) glycols, pentane-1,5-diol, hexane-1,6-diol,hexane-2,4,6-triol, glycerol, 1,1,1-trimethylolpropane, pentaerythritolor sorbitol.

Suitable aromatic polyols are, for example, mononuclear phenols, such asresorcinol, hydroquinone and N,N-bis(2-hydroxyethyl)aniline, orpolynuclear phenols, such asp,p′-bis(2-hydroxyethylamino)diphenylmethane,bis(4-hydroxyphenyl)methane, 4,4′-dihydroxybiphenyl,bis(4-hydroxyphenyl)sulfone, 1,1,2,2′-tetrakis(4-hydroxyphenyl)ethane,2,2-bis(4-hydroxyphenyl)propane or2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane, and novolaks, obtainable bycondensation of aldehydes, such as formaldehyde, acetaldehyde, chloralor furfuraldehyde, with phenols, such as phenol, or with phenolssubstituted in the nucleus by chlorine atoms or by C₁-C₉alkyl groups,e.g. 4-rhlorophenol, 2-methylphenol or 4-tert-butylphenol, or bycondensation with bisphenols, such as those of the kind mentioned above.

Preference is given to the use of a cresol novolak as phenolic curingagent (b).

Mixtures of curing agents can also be used. Furthermore, it is alsopossible to use mixtures of curing agents in which customary epoxy resincuring agents other than the main curing agents mentioned above are usedas co-curing agents, for example anhydride curing agents.

The ratio of curing agent (b) to epoxy resin (a) can vary within widelimits and is dependent upon the content of epoxy groups in (a) and ofhydroxyl groups in (b) and upon the desired properties of the curablecomposition and of the cured product. In general, about from 0.7 to 1.3mol, preferably from 0.9 to 1.1 mol, of OH groups are used per mol ofepoxy groups. It is, however, also possible to use lesser amounts of OHgroups, optionally with addition of customary epoxy resin curing agentsother than the polyols mentioned above.

As component (c) of the present invention there is used a solid reactionproduct of a carboxylic-acid-group-containing microgel and anitrogen-containing base (microgel-amine adduct). Further detailsrelating to the preparation of such a reaction product, possiblecompositions, preferences, etc. form part of the subject matter of EP-A0 816 393 mentioned hereinbefore and, where relevant to the subjectmatter of the present invention, are hereinbelow taken from thatpublication:

In general terms, microgels are understood to be macromolecules thechain segments of which are crosslinked in the region of the individualcoils by way of covalent bridges. Microgels can be prepared by variousknown polymerisation methods. An advantageous method is emulsionpolymerisation of compounds having polymerisable C—C double bonds in thepresence of so-called polyfunctional crosslinking agents, for example bythe seeding technique. After such polymerisation, the microgel particlesare present in the form of an aqueous emulsion or suspension. Thefurther reaction with the nitrogen-containing base can be performedpreferably using such an emulsion/suspension. It is, however, alsopossible first to isolate the microgel in the form of a solid powder,for example by spray-drying or freeze-drying, or to convert the aqueousemulsion into an organic phase by solvent exchange.

Any compound containing at least two polymerisable C—C double bonds can,in principle, be used as the polyfunctional crosslinking agent. In thatcase, intramolecularly crosslinked copolymers, in general havingparticle sizes in the nanometre range (about 5-1000 nm), are formed.

A preferred microgel for the preparation of the reaction product is acopolymer of at least one unsaturated carboxylic acid and at least onepolyfunctional crosslinking agent.

An especially preferred microgel is a copolymer of at least oneunsaturated carboxylic acid, at least one vinyl monomer containing nocarboxylic acid groups and at least one poly-functional crosslinkingagent.

Any carboxylic acid that contains a polymerisable C—C double bond is, inprinciple, suitable for the preparation ofcarboxylic-acid-group-containing microgels.

Preferred unsaturated carboxylic acids are acrylic acid, methacrylicacid, 2-carboxyethyl acrylate, 2-carboxyethyl methacrylate, phthalicacid mono(2-acryloylethyl) ester, phthalic acidmono(2-methacryloylethyl) ester, maleic acid, maleic acid monomethylester, maleic acid monoethyl ester, fumaric acid, fumaric acidmonomethyl ester, fumaric acid monoethyl ester, itaconic acid, cinnamicacid, crotonic acid, 4-vinylcyclohexanecarboxylic acid,4-vinylphenylacetic acid and p-vinylbenzoic acid.

Acrylic acid and methacrylic acid are especially preferred.

Any compound containing at least two polymerisable C—C double bonds is,in principle, suitable as the polyfunctional crosslinking agent. Alsosuitable as polyfunctional crosslinking agents are mixtures of at leasttwo vinyl monomers, e.g. methacrylic acid and glycidyl meth-acrylate,which are able to react with one another by way of additional functionalgroups during or after the polymerisation reaction.

It is preferred to use as the polyfunctional crosslinking agent apolyfunctional acrylic acid ester or methacrylic acid ester of analiphatic, cycloaliphatic or aromatic polyol, an addition product ofacrylic acid or methacrylic acid and a polyglycidyl compound, anaddition product of acrylic acid or methacrylic acid and glycidylacrylate or glycidyl methacrylate, an acrylic acid alkenyl ester ormethacrylic acid alkenyl ester, a dialkenylcyclohexane or adialkenylbenzene.

Especially preferred polyfunctional crosslinking agents are ethyleneglycol diacrylate, ethylene glycol dimethacrylate, propylene glycoldiacrylate, propylene glycol dimethacrylate, 1,4-butanediol diacrylate,1,4-butanediol dimethacrylate, polyethylene glycol diacrylate,polyethylene glycol dimethacrylate, polypropylene glycol diacrylate,polypropylene glycol dimethacrylate, 1,1,1-trimethylolpropanetriacrylate, 1,1,1-trimethylolpropane trimethacrylate, bisphenol Adiglycidyl ether diacrylate, bisphenol A diglycidyl etherdimethacrylate, acrylic acid allyl ester, methacrylic acid allyl ester,divinylcyclohexane and divinylbenzene.

The monomer mixture used for the preparation of the microgels maycomprise one or more vinyl monomer(s) containing no carboxylic acidgroups, for example butadiene and butadiene derivatives, acrylonitrile,methacrylonitrile, acrylic acid esters and acrylic acid amides,methacrylic acid esters and methacrylic acid amides, vinyl ethers andvinyl esters, allyl ethers and allyl esters, styrene and styrenederivatives.

Preferred vinyl monomers containing no carboxylic acid groups are alkylesters, hydroxyalkyl esters and glycidyl esters of unsaturatedcarboxylic acids and styrene derivatives.

Especially preferred carboxylic-acid-group-free vinyl monomers aremethyl acrylate, methyl methacrylate, ethyl acrylate, ethylmethacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate,butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexylmethacrylate and styrene.

The reaction product is prepared preferably from a microgel that is acopolymer of from 2 to 70% by weight of at least one unsaturatedcarboxylic acid, from 0 to 96% by weight of at least one vinyl monomercontaining no carboxylic acid groups and from 2 to 70% by weight of atleast one polyfunctional crosslinking agent, the sum of the percentageamounts by weight always being 100.

Especially preferred microgels are copolymers of from 5 to 50% byweight, especially from 10 to 40% by weight, of at least one unsaturatedcarboxylic acid, from 0 to 90% by weight, especially from 30 to 85% byweight, of at least one vinyl monomer containing no carboxylic acidgroups and from 5 to 50% by weight, especially from 5 to 30% by weight,of at least one polyfunctional crosslinking agent.

The reaction products are referred to hereinbelow simply as“microgel-amine salts”, the term “amine” in this context beingunderstood in the very general sense of “nitrogen-containing base” andnot being limited to the meaning of the term “amine” in the strictersense.

Any basic compound containing at least one basic nitrogen atom is, inprinciple, a suitable nitrogen-containing base for the preparation ofthe reaction products. Examples thereof include aliphatic,cycloaliphatic and aromatic amines and saturated and unsaturatedN-heterocycles.

Primary, secondary and tertiary amines can be used; it is also possibleto use compounds having a plurality of basic nitrogen atoms. Examplesthereof include imidazoles, polyamines, such as triethylenetetramine andisophorone diamine, polyaminoamides, such as the reaction products ofaliphatic polyamines and dimerised or trimerised fatty acids, as well aspolyoxyalkyleneamines, such as Jeffamine® (Texaco).

Preference is given to the use of an amine, a polyamine or an imidazole.

Mixtures of amines and imidazoles are of course also suitable.

Especially preferred nitrogen-containing bases are the amines andimidazoles of formula I, II or III

NR₁R₂R₃  (I),

R₄R₅N—A—NR₆R₇  (II),

wherein R₁ to R₇ are each independently of the others hydrogen,C₁-C₁₂alkyl, unsubstituted or substituted phenyl, benzyl, phenylethyl,cyclopentyl or cyclohexyl, or R₂ and R₃, or R₄ and R₅, or R₆ and R₇,together are tetramethylene, pentamethylene, —(CH₂)₂—O—(CH₂)₂— or—(CH₂)₂—NH—(CH₂)₂—,

A is C₁-C₃₀alkanediyl,

R₈ to R₁₁ are each independently of the others hydrogen, C₁-C₁₈alkyl,phenyl or benzyl, or R₈ and R₉, or R₈ and R₁₁, or R₁₀ and R₁₁, togetherare tetramethylene, pentamethylene, —(CH₂)₂—O—(CH₂)₂— or—(CH₂)₂—NH—(CH₂)₂—.

Examples of amines of formula I include trimethylamine, triethylamine,phenyidimethylamine, diphenylmethylamine, triphenylamine, benzylamine,N,N-dimethylbenzylamine, pyrrolidine, N-methylpyrrolidine,N-methylpiperidine and N-phenylpiperidine.

Suitable diamines of formula II are, for example, 1,2-diaminoethane andN,N,N′,N′-tetramethyl-1,2-diaminoethane.

Examples of imidazoles of formula III include imidazole,1-methylimidazole, 2-methylimidazole, 2-phenylimidazole,2-isopropylimidazole, 2-dodecylimidazole, 2-heptadecylimidazole and2-ethyl-4-methylimidazole.

2-Phenylimidazole, 2-isopropylimidazole, 2-dodecylimidazole,2-heptadecylimidazole and 2-ethyl-4-methylimidazole are especiallypreferred nitrogen-containing bases.

The reaction of the nitrogen-containing base with thecarboxylic-acid-group-containing microgel is preferably performed insolution. Preferred solvents are water and mixtures of water withwater-miscible solvents, for example methanol, ethanol, isopropanol andacetone. The emulsion or suspension obtained on preparation of themicrogel by emulsion polymerisation can be used directly in thereaction. The reaction temperatures are advantageously from 0 to 200°C., preferably from 10 to 100° C. The relative proportions of thestarting materials can vary within wide limits. Advantageously, however,the carboxylic-acid-group-containing microgel and nitrogen-containingbase are used in amounts such that the COOH groups are present inequimolar amounts or in excess relative to basic nitrogen atoms. Thenumber of basic nitrogen atoms is preferably from 5 to 100 mol %,especially from 30 to 100 mol % and more especially from 60 to 95 mol %,based on the number of COOH groups in the microgel.

The microgel-amine salt can be isolated as a solid powder byspray-drying or lyophilisation. It is, however, also possible for theemulsion/suspension to be coagulated using known methods (electrolyteaddition, freezing out) and for the precipitated product to be isolated,by filtration, in the form of a solid substance which can optionally beconverted into the desired particle size by further pulverisation. Theproduct can also be obtained by evaporating the emulsion to dryness andconverting the residue into the desired form by known methods.

For the present invention, the microgel-amine salts are used exclusivelyin solid form. As mentioned at the beginning, the microgel-amine salts(c) are suitable as curing agents or, especially, as curing acceleratorsfor epoxy resins (a). The relative proportions of components (a) and (c)in the compositions according to the invention can vary within widelimits. The optimum ratio is dependent upon, inter alia, the type ofamine and the amine content of the microgel-amine salt and upon thedesired reactivity of the composition, and can be readily determined bythe person skilled in the art.

The ratio by weight of component (a) to component (c) is advantageouslyfrom 1:2 to 2000:1, preferably from 1:1 to 1000:1 and especially from2:1 to 1000:1, when (c) is used as accelerator.

The compositions according to the invention may optionally comprisefurther known accelerators, for example imidazoles orbenzyldimethylamine.

Furthermore, the curable mixtures may comprise tougheners, for examplecore/shell polymers or the elastomers or elastomer-containing graftpolymers known to the person skilled in the art as rubber tougheners.

Suitable tougheners are described, for example, in EP-A-449 776.

For many applications preference is given to compositions that, inaddition to comprising components (a), (b) and (c) described above, alsocomprise filler (d).

Accordingly, the present invention further relates to curablecompositions comprising

(a) an epoxy resin having, on average, more than one 1,2-epoxy group permolecule,

(b) a polyol as epoxy resin curing agent,

(c) a microgel-amine adduct as accelerator, and

(d) filler.

Suitable fillers (d) for the curable mixtures include all known mineraland organic types, for example metal powder, wood flour, carbon black,glass fibres, glass powder, glass beads, Kevlar; semi-metal and metaloxides, such as SiO₂ (Aerosils, quartz, quartz powder, fused silicapowder, aluminium oxide, titanium oxide and zirconium oxide; metalhydroxides, such as Mg(OH)₂, Al(OH)₃ and AlO(OH); semi-metal and metalnitrides, for example silicon nitride, boron nitride and aluminiumnitride; semi-metal and metal carbides (SiC and boron carbides); metalcarbonates (dolomite, chalk, CaCO₃); metal sulfates (barytes, gypsum);zinc sulfide; ground minerals, e.g. of hydromagnesite and huntite, andnatural or synthetic minerals chiefly of the silicate series, e.g.zeolites (especially molecular sieves), talcum, mica, kaolin, Sillitin,wollastonite, bentonite and others.

In order to improve the mechanical properties and the surface quality itis also possible to use variants of the above-mentioned fillers that arecoated with additives, in particular adhesion promoters. For surfacetreatment, preference is given to the use of silanes and acrylates. Anespecially preferred variant is silanisation using theepoxy-group-containing silane Silquest® A-187(gamma-glycidoxypropyltrimethoxysilane from Osi Specialities).

Preferred fillers for the compositions according to the invention arewollastonite and/or a mixture of quartz and kaolinite.

Wollastonite is a naturally occurring calcium silicate of formulaCa₃[Si₃O₉] which has an acicular shape, as does also artificiallyproduced wollastonite. Wollastonite is commercially available, forexample under the name Nyad® from the Nico company. It is preferred touse in the compositions according to the invention wollastonite havingan average particle size of less than 50 μm, preferably less than 5 μm,in amounts of from 1 to 80% by weight, preferably from 25 to 40% byweight, based on the total composition consisting of components (a),(b), (c) and (d).

Quartz/kaolinite mixtures are known and can be produced by simply mixingground quartz with kaolinite. Kaolinite, a major constituent of kaolin,is commercially available as microcrystalline aluminium silicate.

It is preferred to use in the compositions according to the inventionquartz/kaolinite mixtures having an average particle size of less than50 μm, preferably less than 5 μm, and a ratio by weight of quartz tokaolinite of from 5:95 to 95:5, preferably from 20:80 to 80:20, inamounts of from 1 to 80% by weight, preferably from 25 to 40% by weight,based on the total composition consisting of components (a), (b), (c)and (d).

The amounts of fillers can vary within wide limits depending upon theapplication and are from 1 to 80% by weight, based on the total mixtureof components (a), (b), (c) and (d).

In addition to the fillers mentioned above, the curable mixtures mayalso comprise further customary additives, e.g. solvents, reactivediluents, antioxidants, light stabilisers, plasticisers, dyes, pigments,thixotropic agents, toughness improvers, antifoams, antistatics,adhesion agents, parting agents, hydrophobising agents, lubricants andmould-release agents.

The compositions according to the invention can be produced inaccordance with known methods using known mixing apparatus, for examplestirrers, kneaders, rollers or dry mixers. In the case of solid epoxyresins, the dispersing can also be carried out in the melt. Thetemperature during dispersing should be so selected that prematurecuring does not occur during the mixing process. The optimum curingconditions are dependent upon the microgel, the nature and amount of thenitrogen-containing base, on the epoxy resin and on the form ofdispersing and can in each case be determined by the person skilled inthe art using known methods.

Component (c), which is present in the form of a solid, is dispersed inthe epoxy resin (a) or in a solution of the epoxy resin (a) using knownmethods, for example by simply stirring or by stirring with the aid ofglass beads, the operation advantageously being carried out below thetemperature at which the reaction of the microgel-amine salt with theepoxy resin starts. The operation is preferably carried out attemperatures below 60° C.

Component (c) can also be dispersed in the curing agent (b).

The curing of the epoxy resin compositions according to the invention toform mouldings, coatings or the like is carried out in a mannercustomary in epoxy resin technology, for example as described in“Handbook of Epoxy Resins”, 1967, by H. Lee and K. Neville.

Because of the high latency of the microgel-amine salts according to theinvention, the curable compositions have high storage stability and along pot life, and also a high degree of stability with respect tostrong mechanical influences (shear loads, compressive loads). Theimproved storage stability compared with conventional accelerators makesit possible, for example, to prepare one-component epoxy resin/curingagent systems or epoxy resin systems that have improved storagestability without cooling and/or that allow plasticising at relativelyhigh temperatures without the reaction progressing significantly. Suchcompositions according to the invention remain flowable for longer, forexample during plasticising processes, with only slight effects on thereactivity at curing temperature.

The compositions according to the invention are, in principle, suitablefor any area of application in which epoxy resins are cured usingpolyols, for example as casting resins, laminating resins, adhesives,compression moulding compounds, coating compositions, encapsulatingsystems or as a replacement for ceramics, these being, for example: theencapsulation and impregnation of electrical components, such as coils,switches, relays, transformers, bushings, printer magnets, sensors,stators and rotors, and also for the manufacture of various mechanicalcomponents, such as housings, headlights, commutators, pumps and valveparts, pressurised housings, flanges, operating levers and insulators.

The present invention accordingly relates also to the crosslinkedproducts, for example moulded articles, coatings or adhesive bondings,obtainable by curing a composition according to the invention.

EXAMPLES 1. Preparation of Carboxylic-acid-group-containing MicrogelsExample 1.1 Microgel of Methacrylic Acid, Methyl Methacrylate, EthyleneGlycol Dimethacrylate and Trimethylolpropane Trimethacrylate

First, a monomer mixture of 17.05 g of methacrylic acid, 42.07 g ofmethyl methacrylate, 7.51 g of ethylene glycol dimethacrylate and 7.51 gof trimethylolpropane trimethacrylate is prepared.

In a sulfonating flask equipped with a glass anchor stirrer,thermometer, gas connection and feed connection, 2.25 g of sodiumdodecylsulfate and 422.3 g of deionised water are stirred (about 200rev/min) under nitrogen and heated to 65° C. (internal temperature).Then 7.4 ml of the monomer mixture described above and a solution of0.033 g of sodium persulfate in 0.6 ml of deionised water are added. Themixture so obtained is heated to 65° C. and, after stirring for 15 mins.at 65° C., the remainder of the monomer mixture is added over the courseof about 1 hour. After stirring at 65° C. for a further 75 minutes, asolution of 0.033 g of sodium persulfate in 0.6 ml of deionised water isadded. The reaction mixture is stirred at 65° C. for a further 5.5hours. After cooling to room temperature, the contents of the reactionvessel are filtered through a paper filter. The emulsion so obtained hasa solids content of 14.3% and an acid content of 0.408 mol/kg and can bedirectly reacted with an amine or imidazole to form a microgel-aminesalt.

2. Preparation of Microgel-amine Salts Example 2.1

A solution of 17.08 g of 2-ethyl-4-methylimidazole in 44 g ofisopropanol is added, with stirring, to 400 g of the aqueous emulsionprepared according to Example 1.1. The resulting emulsion of amicrogel-imidazole salt is spray-dried (inlet temperature: 132° C.,outlet temperature: 85° C.). The microgel-imidazole powder is furtherdried for 8 hours at 70° C. in vacuo (20 mbar) and has an amine contentof 1.96 mol/kg and an acid content of 2.01 mol/kg.

3. Preparation of a Composition According to the Invention andComparison Examples Example 3.1 (Example of the Invention)

334.40 g of a solid epoxy cresol novolak resin having an epoxy contentof from 4.3 to 4.9 mol/kg; 163.20 g of a cresol novolak having ahydroxyl content of from 8.0 to 9.0 mol/kg, obtainable from OccidentalChem., Belgium, under the trade name Durez® 33009; 21.92 g ofmicrogel-imidazole accelerator according to Example 2.1; 562.08 g ofwollastonite having an average particle size of less than 4.5 μm,obtainable from Nyco, USA, under the trade name Nyad® 1250; 488.00 g ofa quartz/kaolinite mixture having an average particle size of 1.8 μm,obtainable from Hoffmann & Söhne, Germany, under the trade name Aktisil®EM; 6.40 g of carbon black (Elftex 460); 12.80 g of OP Wax 125 U fromHoechst and 9.60 g of calcium stearate are ground in a ball mill, thencompounded on a calender (Schwabenthan) at a temperature of from 100 to110° C. and ground to form granules.

To determine the viscosity and the curing time under process conditions,34 g of granules are tested in a measuring kneader (BrabenderPlasticorder GU 1315/2 type) at a paddle speed of 30 rpm, the so-calledB value (torque in Nm) being used as a measure of the viscosity and theAD value as a measure of the curing time (time in seconds fromintroduction of the sample to curing).

The granules yield the following values:

120° C. 160° C. B value 3.5 Nm 0.6 Nm AD value 876 sec 127 sec

The ratio between the AD values at 120° C. and 160° C. is 6.9, therebydemonstrating good latency.

From the granules there are produced, on chrome-plated tools, ISO bars(80×10×4 mm) over the course of 4 minutes at 170° C. and Tg plates(60×10×1 mm) over the course of 3 minutes at 170° C.

The following properties of the mouldings obtained were measured:

flexural strength (ISO 178/93) 95.9 MPa modulus of elasticity (ISO178/93) 13087 MPa impact strength (ISO 179-1eU/93) 5.4 KJ/m² glasstransition temperature (ISO 6721/94) 214° C.

Example 3.2 (Comparison Example)

For comparison with Example 3.1, a standard system is prepared,characterised in that 2-ethylimidazole is used as accelerator instead ofthe microgel-imidazole accelerator in Example 3.1. Otherwise, theExample has the same composition as in Example 3.1. The granulesproduced analogously to Example 3.1 have an AD value ratio of 3.4.

Example 3.3 (Comparison Example; Use of an Anhydride Curing Agent)

541.5 g of a solid bisphenol A epoxy resin having an epoxy content offrom 1.68 to 1.75 equivalents/kg; 1088.3 g of a solid bisphenol A epoxyresin having an epoxy content of from 1.33 to 1.40 equivalents/kg; 285.0g of an anhydride curing agent; 102.0 g of microgel-imidazoleaccelerator according to Example 1.2; 5378.3 g of quartz having anaverage particle size of less than 7.0 μm, obtainable from Sihelco underthe trade name B300; 30.0 g of carbon black (Elftex 460) and 75.0 g ofOP Wax 125 U from Hoechst are ground in a ball mill, then compounded ona kneader (Werner—Pfleiderer) at a temperature of up to 90° C. andground to form granules.

To determine the viscosity and the curing time under process conditions,34 g of granules are tested in a measuring kneader (BrabenderPlasticorder GU 1315/2 type) at a paddle speed of 30 rpm, the so-calledB value being used as a measure of the viscosity and the AD value as ameasure of the curing time (time in seconds from introduction of thesample to curing).

The granules yield the following values:

120° C. 160° C. B value 1.3 Nm 0.3 Nm AD value 638 sec 116 sec

The ratio between the AD values at 120° C. and 160° C. is 5.5, therebydemonstrating good latency.

Example 3.4 (Comparison Example)

For comparison with Example 3.3, a standard system is produced,characterised in that 2-ethylimidazole is used as accelerator instead ofthe microgel-imidazole accelerator in Example 3.3. Otherwise, theExample has the same composition as in Example 3.3. The granulesproduced analogously to Example 3.3 have an AD value ratio of 4.5.

The following Table gives an overview of the compositions and the ADratios determined in each of tests 3.1 to 3.4:

test 3.1 3.2 3.3 3.4 resin epoxy cresol epoxy cresol DGEBA DGEBA novolaknovolak curing agent cresol novolak cresol novolak anhydride anhydrideaccelerator microgel imidazole microgel imidazole AD ratio 6.9 3.4 5.54.5

In principle, it is more difficult to establish latent full-curingbehaviour in the case of highly functional systems (tests 3.1 and 3.2,“novolak systems”) consisting of epoxy novolaks and novolak curingagents than is the case with comparatively less functional systems(tests 3.3 and 3.4, “anhydride systems”), the reason being that, in thecase of highly functional systems, there is already significantcrosslinking when the reaction has progressed only slightly, whereas inthe case of the anhydride systems initially only linear structures areformed. That is documented by the fact that, where the measured ADratios are used as a measure of the latency, the AD ratio drops from 4.5to 3.4 (see tests 3.4 and 3.2). The Table also shows that, in the caseof an anhydride system, an improved latency behaviour can be achieved byreplacing an imidazole with a microgel in accordance with the invention.The AD ratio then improves from 4.5 to 5.5. The novolak/microgel systemaccording to the invention (test 3.1) surprisingly then exhibitssignificantly more latent behaviour than expected. A person skilled inthe art who, for application-related reasons, wishes to use a lesslatent system has a very wide range of possibilities for producing thesystem according to the invention by including components such as, forexample, those used in the above Comparison Examples according to theproperties desired.

Application Examples 4.1 Production of Components by theInjection-moulding Technique, Using the Example of Headlight Reflectors

The granules prepared according to the above tests 3.1 (according to theinvention) and 3.2 are plasticised in the plasticating cylinder of aninjection-moulding machine at elevated temperature, the temperatures forzones 1 and 2 being 75° C. in each case and the temperature for zone 3being 90° C. Under those conditions, when the system prepared accordingto 3.2 is used, in the event of interruptions in the cycle of more thanas little as 60 seconds the plasticating unit of the injection-mouldingsystem must be run until empty and subsequently restarted. When thesystem according to the invention is used, production can be continued,without a cleaning step, even after interruptions of up to 5 minutes. Inthe manufacture of headlight reflectors by the injection-mouldingtechnique, excess injected material and residues remaining after removalfrom the mould, especially on the highly structured rear wall of thereflector, can make it continually necessary to blow out or clean themould in a separate operation. Such variations between shots can bebetter tolerated by a latent material as described in test 3.1, becausethe reaction progresses only slightly in the plasticating cylinder.Consequently, it is possible for the process to proceed more stably,with less waste.

4.2 Impregnating Moulding Compound Using the Example of the Impregnationof Coils

a) Preparation of the Impregnating Compound

464.8 g of wollastonite having an average particle size of less than 2μm (mesh grade 200, obtainable from Nyco, USA, under the trade nameNyad® 200) and 2.3 g of silane adhesion promoter Silan Silquest® A-187are ground for 30 minutes using a ball mill.

Then the components 151.4 g of a solid epoxy cresol novolak resin havingan epoxy content of from 4.3 to 4.6 mol/kg, 98.5 g of a solid bisphenolA epoxy resin having an epoxy content of from 2.15 to 2.22 mol/kg, 109.1g of a cresol novolak having a hydroxyl content of from 8.0 to 9.0mol/kg, obtainable from Occidental Chem., Belgium, under the trade nameDurez® 33009, 6.7 g of microgel-imidazole accelerator according toExample 2.1, 0.2 g of carbon black (Elftex 460) and 17.0 g of OP® Wax125 U from Hoechst are added and ground in the ball mill for 3 hours.

Finally, 150 g of milled glass fibres (average length=225 μm, averagediameter=15-16 μm, obtainable under the trade name Milled Glas® fromOwens Corning), and the total composition again are ground for 30minutes. The powders so obtained are then compounded on a calender(Schwabenthan) at a temperature of 80° C. and processed to formgranules.

b) Impregnation, Determination of the Depth of Impregnation, Assessmentof the Quality of Impregnation

FIG. 1 shows a view, in diagrammatic form, of the compression tool bymeans of which the test coils are impregnated in the following Examples.FIG. 2 shows a longitudinal section through the coil former used in theExamples and its dimensions.

In all the Examples, the impregnation of the test coil is carried outaccording to the principle of transfer moulding, the test apparatusshown in diagrammatic form in FIG. 1 being used. The apparatus comprisestwo parts (1) and (6), which are separable from one another. The firstpart (1) has an injection chamber (2) for accommodating a tablet (11)consisting of the impregnating composition according to the invention;the transfer plunger (3); the cavity (4); and a bore (5) foraccommodating a temperature sensor. The second part (6) comprises a core(7) for holding the coil (10) being impregnated, an apparatus (8) forremoval of the impregnated coil from the core (7) and a connection (9)for evacuation of the cavity (4). A coil (10) preheated to about 110°C., which has the dimensions shown in FIG. 2 and which has in eachcompartment a winding of copper wire 94 mm in diameter, having a windingdensity of about 100 turns per mm² (the thickness of the windingincreasing, from the topmost compartment to the bottommost compartment,from about 3.5 to about 5.5 mm) is introduced into the cavity (4) of theimpregnating tool (1, 6), which has been preheated to 180° C. Theimpregnating composition in the form of granules is cold-compressed intoa tablet and then heated to about 70° C. with the aid of ahigh-frequency preheating apparatus. The tablet (11) so preheated isintroduced into the injection chamber (2) and a vacuum of about 30 mbaris applied to the cavity. The impregnating compound is then transferredto the cavity (4) with the aid of the plunger (3) over a period of about15 s (injection pressure between 80 and 150 bar). The subsequent curingtime is 5 min. The encapsulated and impregnated coil is then removedfrom the mould. The removed coil is sawn apart in the longitudinaldirection and polished. With the aid of a microscope, the depth ofimpregnation achieved in each case is measured and the quality ofimpregnation is assessed visually, the impregnation being considered“good” if more than 95% of the space between the turns of wire in awinding are filled with the impregnating compound.

In accordance with the described procedure, 500 grams of an impregnatingcompound of the above composition are prepared and tested. Theimpregnating compound has the following properties:

property depth of impregnation [mm] 4.0 quality of impregnation goodtime to reach Shore-D hardness of 70 3 min

Using the formulation according to the invention, it is consequentlypossible to achieve an extensive depth of impregnation of 4 mm whileachieving a good quality of impregnation. A Shore-D hardness of 70,necessary for removing the coil from the mould, is achieved after only 3min. A reduction in production costs can be achieved by means of suchfast-curing moulding compounds.

4.3 Multi-stage Build-up of a Rod-like Ignition Coil

Industry is calling for ever smaller diameters in the manufacture ofrod-like ignition coils. As a result, the encapsulation and impregnationespecially of the inner coil in a so-called “one-shot” process isbecoming increasingly difficult. That is especially the case because itis imperative to avoid inclusions of air and to obtain an evendistribution of the moulding compound.

As a result of the good impregnating properties—described in section4.2—of the moulding compounds according to the invention, it is possibleto build up rod-like ignition coils in several stages.

First the metal core of a coil can be so encapsulated with the mouldingcompound that the outer contour forms a coil former for the innerwinding of a rod-like ignition coil (see FIG. 3; moulding compoundcorresponds to the black area).

After the wire winding has been applied, it can be encapsulated, andimpregnated, in a second step. The inner coil former can be either theprimary or the secondary winding, as indicated in the lower half andupper half of the figure, respectively. The outer contour of themoulding forms the coil former for the second, complementary winding(see FIG. 4; moulding compound corresponds to the black area).

In a third step, the outer winding can then also be impregnated andencapsulated. The outer shape is identical to the outer contour of therod-like ignition coil, assuming that no further additions (e.g. forelectrical screening) are provided (see FIG. 5; moulding compoundcorresponds to the hatched area).

Industry is calling for ever smaller diameters in the manufacture ofrod-like coils. As a result, the encapsulation and impregnationespecially of the inner coil in a so-called “one-shot” process isbecoming increasingly difficult. That is especially the case because itis imperative to avoid inclusions of air and to obtain an evendistribution of the moulding compound. A multi-stage procedure firstlyhas the advantage that very small spacings between the inner and outercoils can be achieved whilst providing a high degree of freedom ofdesign, for example in the wire diameter or in the type and position ofthe windings. Secondly, the thermoplastic coil formers that arecustomary today can be replaced by the moulding compound according tothe invention, bringing about a reduction in transitions betweendielectrics and, therefore, in potential partial discharges.

What is claimed is:
 1. A composition comprising (a) an epoxy resinhaving, on average, more than one 1,2-epoxy group per molecule, (b) apolyol as epoxy resin curing agent and (c) a solid reaction product of acarboxylic-acid-group-containing microgel and a nitrogen-containing base(microgel-amine adduct) as accelerator.
 2. A composition according toclaim 1, comprising, as epoxy resin (a), an aromatic epoxy resin.
 3. Acomposition according to claim 1, comprising, as epoxy resin (a), abisphenol diglycidyl ether or an epoxy novolak.
 4. A compositionaccording to claim 1, comprising, as epoxy resin (a), an epoxy phenolnovolak or an epoxy cresol novolak.
 5. A composition according to claim1, comprising, as epoxy resin curing agent (b), a cresol novolak.
 6. Acomposition according to claim 1, comprising, as solid microgel-amineadduct (c), a copolymer of at least one unsaturated carboxylic acid andat least one polyfunctional crosslinking agent.
 7. A compositionaccording to claim 1, comprising, as additional component (d), a filler.8. A composition according to claim 1, comprising, as additionalcomponent (d), from 1 to 80% by weight filler, based on the totalcomposition consisting of components (a), (b), (c) and (d).
 9. Acomposition according to claim 1, comprising, as component (d), from 1to 80% by weight wollastonite, based on the total composition consistingof components (a), (b), (c) and (d), having an average particle size ofless than 50 μm.
 10. A composition according to claim 1, comprising, asadditional component (d), from 25 to 40% by weight wollastonite, basedon the total composition consisting of components (a), (b), (c) and (d),having an average particle size of less than 5 μm.
 11. A compositionaccording to claim 1, comprising, as additional component (d), from 1 to80% by weight quartz/kaolinite mixture, based on the total compositionconsisting of components (a), (b), (c) and (d), having an averageparticle size of less than 50 μm and a ratio by weight of quartz tokaolinite of from 5:95 to 95:5.
 12. A composition according to claim 1,comprising, as additional component (d), from 25 to 40% by weightquartz/kaolinite mixture having an average particle size of less than 5μm and a ratio by weight of quartz to kaolinite of from 20:80 to 80:20.13. A crosslinked product obtainable by curing a composition accordingto any one of claims 1 to
 12. 14. The composition of claim 1, whereinthe epoxy resin is a solid resin.
 15. The composition of claim 14,wherein the solid epoxy resin is an epoxy cresol novolak.